No, no. Forget about Fire Dragon's post, all your need is your HALF LIFE CD KEY to install Steam. Grab it at
www.steampowered.com. Then you have to create an account using your e-mail address. After you have done this, register Half Life by entering your CD Key by clicking on the 'Browse Games' section on the main menu of Steam.
After you entered the CD Key, you'll be able to download Half Life THROUGH Steam, WITHOUT using your original CD. Run it at least ONCE, THEN install ESF 1.2, and THEN install ESF 1.2.1. The installer will AUTOMATICALLY find your Steam folder and install the mod, if it doesn't, you don't have Steam (example of where it might be installed: C: \Program Files\Valve\Steam\Steamapps\
[email protected]\Half-Life\).
When your all finished, your 'My Games' list will look like this: